Cigarette filling optical control method

Abstract: The filling of a cigarette (3) is controlled by detecting a brightness curve (18; 37) of at least one part of the open end of the cigarette (3), processing the resulting brightness curve (18; 37) to obtain a contrast index, and comparing the resulting contrast index with an equivalent index of a correctly filled cigarette (3) to obtain a signal indicating acceptance of the cigarette (3) under observation.

Description: The present invention relates to a cigarette filling optical control method. More specifically, the present invention relates to a method of controlling the conformation of the open end of cigarettes and, in particular, the presence or absence of tobacco at the open end, on a cigarette manufacturing machine and/or filter assembly machine and/or packing machine. At the output of a cigarette manufacturing machine and/or filter assembly machine and/or at the input of a packing machine, the cigarettes are normally subjected to numerous checks comprising a check of the filling to determine the presence or absence of tobacco at the open end of the cigarettes. In most cases, filling control consists in illuminating the front surface of the open end of the cigarette by means of a light source; forming an image of the front surface by means of a detecting unit featuring a telecamera or equivalent optical monitoring system; and transmitting the image to a comparing unit for comparing it with a specimen image and emitting a reject signal in the event the detected and specimen images differ over and above a given limit. In general, the difference in the detected and specimen images depends on differences in shading which, as is known, varies according to the presence of gaps on the front surface due to the absence of tobacco. Unfortunately, the shading of the detected image has been found to depend largely, not only on the presence of gaps, but also on the colour of the tobacco employed, so that known devices of the above type involve expensive, time-consuming setup procedures whenever the type of tobacco is changed. FR-A-2,312,975 shows a filling control device, according to which filling control consists in illuminating the front surface of the open end of the cigarette by means of a light source; detecting by a sensor the brightness reflected by the open end; transforming the detected brightness in an electric signal to be compared with a threshold value; and correcting the electric signal by a further signal, which keep in account the distance between the cigarette end and the sensor. The above filling control has proved to be unsatisfactory because the sensor detects the overall brightness reflected by a cigarette open end without distinguishing different areas of the open end. This fact renders the above filling control particularly ineffective when the color of tobacco varies. According to a device shown in GB-B-1,112,687, the filling control consists in illuminating the front surface of the open end of the cigarette by means of a light source; forming an image of the front surface by means of a detecting unit; and scanning the image with an electron beam in order to detect, on the image, dark spots, which correspond to Voltage drops in the electron beam. Also the above filling control has the drawbacks discussed hereinbefore since cannot distinguish the gaps form the different colour. In addition to that, the above filling control cannot be employed in the modern manufacturing machines and/or in the filter assembly machines and/or in the packing machines because the high travelling speed of cigarettes in these modern machines renders impossible to scan the complete image for each cigarette, and such a control would result incomplete. Moreover, the device for implementing the filling control described above is complicated and costly. It is an object of the present invention to provide a straightforward, low-cost optical control method designed to overcome the aforementioned drawbacks. According to the present invention, there is provided a cigarette filling optical control method according to claim 1. The method preferably comprising a further stage for mechanically or electrically controlling the position of the cigarette under observation in relation to the reference plane. A non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows a preferred embodiment of the optical device according to the present invention; Figure 2 shows a partial view of the Figure 1 device in two different operating situations; Figure 3 shows a working diagram of a brightness curve detected by means of the Figure 1 optical device; Figure 4 shows a further working diagram of the contrast index curve formed by processing the Figure 3 curve; Figure 5 shows a schematic view of a variation of the Figure 1 optical device; Figures 6 and 7 show schematic views of a first and second perfected embodiment of the optical devices in Figures 1 and 5; Figure 8 shows a working diagram of an alternative brightness curve detected by means of the Figure 1 optical device; Figure 9 shows a variation of a portion of Figure 1, relative to an optical device employing the Figure 8 brightness curve. Number 1 in Figure 1 indicates an optical device for controlling the filling of the open end portion 2 of a cigarette 3. Device 1 comprises a light source 4 for emitting a beam 5 impinging on and illuminating the front end surface 6 of portion 2; and a biconvex lens 7 presenting an optical axis 8 and a fixed focus 9. As shown in Figure 2, device 1 presents a reference plane consisting of a fixed focusing plane 10 a given distance A from lens 7, and a substantially zero depth of field. As shown in Figure 1, cigarette 3 is preferably, but not necessarily, engaged by a mechanical guide device 11 defined by a front and rear wall 12, 13 parallel to plane 10, and along which each cigarette 3 is fed transversely by a known conveyor device (not shown) into a control position coaxial with axis 8. Wall 12 is made of transparent material with an inner surface coincident with plane 10; and wall 13 is separated from wall 12 by a distance approximately equal to but no less than the length of cigarette 3, and presents a lead-in portion 14 for exerting axial thrust on cigarette 3, as this is fed into said control position, so that the annular front end edge 15 defined by the wrapping paper of cigarette 3 is positioned tangent to plane 10. Lens 7 forms part of a detecting device 16 which also comprises a sensor 17 located along axis 8, on the opposite side of focus 9 to lens 7, on the opposite side of lens 7 to cigarette 3, and at a given distance B (Figure 2) from lens 7, for supplying in known manner a brightness curve 18 (Figure 3) relative to at least part of the image of surface 6 observed through lens 7. Sensor 17 may consist of a CCD sensor, or one or more linear sensors for analyzing fixed linear portions of tobacco-filled surface 6, i.e. the surface within edge 15. Device 1 also comprises a known differentiating block 19 for processing curve 18 to obtain a contrast curve (not shown) which is in turn processed by a known index generating block 20 to obtain a contrast index of the image observed by sensor 17. In a known comparing block 21, the resulting contrast index is compared with a reference index (e.g. the mean contrast index of the last 1000 cigarettes 3 examined) supplied to block 21 by an emitter 22, to obtain a signal which is sent to a threshold circuit 23 for emitting a reject signal in the event the contrast index of cigarette 3 and said reference index differ by an amount greater than a predetermined value. In actual use - and with reference to the Figure 4 curve 24 showing the variation in the contrast index alongside a variation in the distance of surface 6 from focusing plane 10 - when end portion 2 is completely and properly flat, i.e. surface 6 is a flat surface coplanar with edge 15 and plane 10 (Figure 2a), block 20 emits a signal corresponding to a maximum value D of the contrast index. The same does not apply, however, in the event portion 2 presents gaps (Figure 2b) so that surface 6 is no longer coplanar with edge 15 and plane 10. In this case, in fact, as device 1 presents a substantially zero depth of field, the signals emitted by block 20, and indicating the value of the contrast index, indicate a reduction in the contrast index (curve 24) in direct proportion to the distance between surface 6 and plane 10. If C is the reference index value, circuit 23 emits a reject signal when the difference between value C and the detected value E exceeds a given value. In the Figure 5 variation, the beam 5 emitted by source 4 and reflected by surface 6 is directed onto a semireflecting mirror 25 which reflects a first portion of beam 5 to form a beam 5a directed towards a first optical device 26a, and lets through a second portion of beam 5 to define a beam 5b which is directed by a fully reflecting mirror 27 towards a second optical device 26b. Optical devices 26 are substantially similar to device 1, and comprise respective focusing lenses 28a, 28b similar to lens 7 and having respective fixed focusing planes 10a, 10b on either side of and symmetrical in relation to a reference plane 10. Plane 10, which defines the correct plane of edge 15 of cigarette 3, may therefore be said to be equally out of focus in relation to lenses 28a, 28b. Like device 1, devices 26a, 26b comprise respective sensors 17, respective differentiating blocks 19, and respective contrast index generating blocks 20, the output signals of which are supplied to a comparing block 29. The output signal of block 29 presents a value depending on the difference between said two indexes, and is supplied to a threshold circuit 30 for emitting a reject signal when said output signal exceeds a given value. That is, if surface 6 is substantially coplanar with edge 15 and hence with plane 10, the two output signals from blocks 20 cancel each other out, whereas the output signal from block 29 increases in proportion to the amount by which surface 6 is shifted, in relation to plane 10, towards one or other of planes 10a, 10b. The signals supplied by devices 1 and 26 are obviously only effective in producing the reject signal if the front edge 15 of cigarette 3 does in fact lie in plane 10, which is definitely assured if provision is made for mechanical guide device 11, as is normally the case on a packing machine, or for other means of maintaining cigarette 3 in the correct observation position described above. In some cases, however, cigarettes 3 fail to assume the correct observation position and are shifted axially in relation to it by varying amounts. Such, for example, is the case shown in Figures 6 and 7 wherein cigarettes 3 are retained by suction, in varying axial positions, inside respective seats 31 on the outer periphery of a feed roller 32, e.g. of a filter assembly machine, and are fed successively by roller 32 through a control station 33 equipped with an optical control device 1, 26. In this case, optical device 1, 26 is associated with a position detector consisting, in the Figure 6 case, of a fixed rear detector 34 for detecting the distance between itself and the end of cigarette 3 opposite portion 2, and, in the Figure 7 case, of a lateral detector 35 for detecting the position of the plane of edge 15 of cigarette 3. The signal emitted by detector 34, 35 is sent to block 20 (or blocks 20) of device 1 (or devices 26) to permit block 20 (or blocks 20) to emit a signal corrected according to the distance between the plane of edge 15 of cigarette 3 and plane 10. As shown in Figure 8, detector 34, 35 may be dispensed with by extending the observation range of sensor 17 to edge 15 and hence to the outer paper layer 36 of cigarette 3, and by processing brightness curve 37, supplied by sensor 17, differently as compared with Figure 1. More specifically, and with reference to Figure 9, the curve 37 signal is sent to differentiating block 19 and hence index generating block 20, as well as in parallel manner to a comparing block 38 which is supplied by a memory 39 with a signal relative to a correct brightness curve 40 (Figure 8). At the points at which the observation line intersects edge 15, curve 40 presents two peaks 41 relative to detection of paper layer 36. Since peaks 41 are relative to the detection of white points in plane 10, identical peaks 41 should be present in any curve 37 relative to a cigarette 3 whose edge 15 lies in plane 10. If they are not, this means edge 15 is shifted in relation to plane 10 by an amount the value of which is indicated by an output signal of block 38; which output signal is used to drive a variable-gain amplifier 42 interposed between the output of block 20 and the input of block 21, for supplying block 21 with a modified contrast index to eliminate the error due to the shift in edge 15 in relation to plane 10.

Claims: A cigarette filling optical control method comprises a stage consisting in detecting at least one brightness curve (18; 37) of at least one part of the open end (2) of the cigarette (3) under observation; the method being characterized by the further stages of processing the brightness curve (18; 37) by means of a differentiating block (19), the output signal of which, corresponding to a contrast curve, is further processed to obtain a contrast index; said brightness curve (18; 37) being detected by means of an optical device (1) presenting a reference plane consisting of a fixed focusing plane (10) of the optical device (1) and being supplied by a sensor (17) of said optical device (1); the sensor (17) receiving a light beam (5) reflected by said open end (2) of the cigarette (3) and focused by a fixed-focus lens (7) presenting said fixed focusing plane (10) and a substantially zero depth of field; and comparing the contrast index with an equivalent given index to obtain a signal indicating acceptance of the cigarette (3) under observation. A method as claimed in Claim 1, characterized in that it provides for detecting two brightness curves (18; 37) by means of two optical devices (26) presenting respective fixed focusing planes (10a, 10b) arranged symmetrically in relation to a reference plane (10). A method as claimed in Claim 2, characterized in that said brightness curves (18; 37) are supplied by respective sensors (17) of the respective optical devices (26); each sensor (17) receiving a respective portion (5a, 5b) of a light beam (5) which is reflected by said open end (2) of the cigarette (3); each said beam portion (5a, 5b) being focused by a respective fixed-focus lens (28a; 28b); each optical device (26) presenting a respective said fixed focusing plane (10) and a substantially zero depth of field; and said indexes of said optical devices (26) being compared with each other. A method as claimed in any one of the foregoing Claims, characterized in that it comprises a further stage consisting in controlling the position of the cigarette (3) under observation in relation to the reference plane. A method as claimed in Claim 4, characterized in that said further control stage in turn comprises a stage consisting in acting, via mechanical means (11), on the cigarette (3) under observation, so that its end (2) is positioned in the reference plane (10). A method as claimed in Claim 4, characterized in that said further control stage in turn comprises a stage consisting in detecting the position of the cigarette (3) under observation in relation 'to said reference plane (10). A method as claimed in Claim 6, characterized in that it comprises yet a further stage consisting in modifying the value of said index as a function of the position of the cigarette (3) under observation in relation to said reference plane (10). A method as claimed in Claim 6 or 7, characterized in that the position of the cigarette (3) under observation in relation to the reference plane (10) is detected via electronic sensor means (34; 35). A method as claimed in Claim 6 or 7, characterized in that the position of the cigarette (3) under observation in relation to the reference plane (10) is detected by extending observation of the open end (2) of the cigarette (3) to a layer (36) of peripheral paper, to obtain a brightness curve (37) presenting two peaks (41) at said layer (36), and by comparing these two peaks (41) with the peaks of a reference curve (40). A method as claimed in any one of the foregoing Claims, characterized in that it also comprises stages consisting in comparing said contrast index with a reference index; and emitting a reject signal in the event the contrast index differs from the reference index by an amount over and above a predetermined value.

Inventors: DI STEFANO GIUSEPPE, GAMBERINI ANTONIO, GHINI MARCO, NERI ARMANDO, DI STEFANO, GIUSEPPE, GAMBERINI, ANTONIO, GHINI, MARCO, NERI, ARMANDO
Applicants: GD SPA, G.D SOCIETA' PER AZIONI
Application year: 1994
Main classification: A24C5
IPC codes: A24C5